A selection of hot subluminous stars in the GALEX survey I. Correlation with the Guide Star Catalog

TL;DR

This study compiles a catalogue of hot subdwarf and white dwarf stars from GALEX, GSC, and 2MASS data, identifying new candidates and providing spectroscopic analysis for a subset, advancing the understanding of these luminous, hot stellar objects.

Contribution

The paper introduces a new catalogue of bright hot subdwarfs and white dwarfs, including newly identified candidates, with spectroscopic confirmation and analysis of their properties.

Findings

Approximately 700 sources identified with UV-optical-IR criteria.

About 120 new hot subdwarf candidates discovered.

Spectroscopic analysis of 52 subdwarfs, including 48 new analyses.

Abstract

We assembled a catalogue of bright, hot subdwarf and white dwarf stars extracted from a joint ultraviolet, optical, and infrared source list. The selection is secured using colour criteria that correlate well with effective temperatures T_eff ~> 12,000 K. We built a N_UV-V versus V-J diagram for more than 60,000 bright sources using the Galaxy Evolution Explorer (GALEX) N_UV magnitude (N_UV<14), and the associated Guide Star Catalog (GSC2.3.2) photographic quick-V magnitude and the Two Micron All Sky Survey (2MASS) J and H magnitudes. This distillation process delivered a catalogue of approximately 700 sources with N_UV-V<0.5 comprising ~160 known hot subdwarf stars and another ~60 known white dwarf stars. A reduced proper-motion diagram built using the proper-motion measurements extracted from the Naval Observatory Merged Astrometric Dataset allowed us to identify an additional ~120 new hot subdwarf candidates and ~10 hot white dwarf candidates. We present a spectroscopic study of a subset of 52 subdwarfs, 48 of them analysed here for the first time, and with nine objects brighter than V ~ 12. Our sample of spectroscopically confirmed hot subdwarfs comprises ten sdO stars and 42 sdB stars suitable for pulsation and binary studies. We also present a study of 50 known white dwarfs selected in the GALEX survey and six new white dwarfs from our catalogue of subluminous candidates. Ultraviolet, optical, and infrared synthetic magnitudes employed in the selection and analysis of white dwarf stars are listed in appendix.